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Xiaogang Liu

Bio: Xiaogang Liu is an academic researcher from National University of Singapore. The author has contributed to research in topics: Medicine & Photon upconversion. The author has an hindex of 94, co-authored 425 publications receiving 41825 citations. Previous affiliations of Xiaogang Liu include Heilongjiang University & Massachusetts Institute of Technology.


Papers
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TL;DR: These results offer an avenue to manipulate the NLO properties of MOFs using interpenetration and provide access to tunable single-crystal NLO devices.
Abstract: Interpenetration in metal-organic frameworks (MOFs) is an intriguing phenomenon with significant impacts on their properties, and functional applications. Herein, we show that a 7-fold interpenetrated MOF (1) is transformed into an 8-fold interpenetrated MOF by the loss of DMF in a single-crystal-to-single-crystal manner. This is accompanied by a giant enhancement of the second harmonic generation (SHG ca. 125 times) and two-photon photoluminescence (ca. 14 times). The strengthened π-π interaction between the individual diamondoid networks and intensified oscillator strength of the molecules aid the augment of dipole moments and boost the nonlinear optical conversion efficiency. Large positive and negative thermal expansions of 1 occur at 30-150 °C before the loss of DMF. These results offer an avenue to manipulate the NLO properties of MOFs using interpenetration and provide access to tunable single-crystal NLO devices.

35 citations

Journal Article
TL;DR: Oxygen/carbon/silicon-rhodamine fluorophores and probes are ubiquitous in bioimaging and biosensing applications and have excellent brightness, photostability, and biocompatibility.
Abstract: Oxygen/carbon/silicon-rhodamine fluorophores and probes are ubiquitous in bioimaging and biosensing applications. Besides excellent brightness, photostability, and biocompatibility, these dyes possess a unique intramolecular spirocyclization equilibrium between nonemissive ring-closed and fluorescent ring-opened forms. Understanding the closed-ring/open-ring switching mechanism is critical for the rational designs of high-performance rhodamine dyes and probes. First-principles calculation-combined data search carried out herein quantitatively elucidates the importance of both substituent groups and environmental conditions in influencing the ring-opening process. Our analysis yields a unified push–pull model in elucidating the ring-opening mechanism of rhodamines. We demonstrate that this model produces excellent agreements with a broad range of experiments that involve different structural modifications in rhodamines and varied environmental conditions (i.e., solvent polarity, hydrogen bond donating strength, and acidity). We foresee that this push–pull model will provide important guidelines for understanding and designing rhodamine dyes and probes with required fluorescence-switching properties, such as autoblinking dyes and photoactivable dyes for super-resolution imaging and fluorogenic dyes for biochemical studies.

35 citations

Journal ArticleDOI
TL;DR: In this paper, the insertion of an indazole unit into ICT scaffold can fully amplify the intramolecular rotation in donor-indazoleπ-acceptor fluorophores, whereas efficiently suppressing the rotation in their EWT-substituted system (fluorescence ON).
Abstract: Intramolecular charge transfer (ICT) is a fundamental mechanism that enables the development of numerous fluorophores and probes for bioimaging and sensing. However, the electron-withdrawing targets (EWTs)-induced fluorescence quenching is a long-standing and unsolved issue in ICT fluorophores, and significantly limits the widespread applicability. Here we report a simple and generalizable structural-modification for completely overturning the intramolecular rotation driving energy, and thus fully reversing the ICT fluorophores' quenching mode into light-up mode. Specifically, the insertion of an indazole unit into ICT scaffold can fully amplify the intramolecular rotation in donor-indazole-π-acceptor fluorophores (fluorescence OFF), whereas efficiently suppressing the rotation in their EWT-substituted system (fluorescence ON). This molecular strategy is generalizable, yielding a palette of chromophores with fluorescence umpolung that spans visible and near-infrared range. This strategy expands the bio-analytical toolboxes and allows exploiting ICT fluorophores for light-up sensing of EWTs including N-acetyltransferases and nerve agents.

35 citations

Journal ArticleDOI
TL;DR: In this article, the halogen bond passivated lead iodide perovskite surface was analyzed and a detailed potential energy surface was constructed by moving the adsorbed molecule along different axes of the unit cell.
Abstract: Organic molecules have recently been used to modify the surface/interface structures of lead halide perovskite solar cells to enhance device performance. Yet, the detailed interfacial structures and adsorption mechanism of the molecular modified perovskite surface remain elusive. This study presents a nanoscopic structural view on how organic molecules interact with the perovskite surface. We focus on the halogen bond passivated lead iodide perovskite surface, based on first-principles calculations. Our calculations show that organic molecules can interact with the perovskite surface via halogen bonds, which modifies the interfacial structures of the perovskite surface. We also constructed a detailed potential energy surface of the perovskite surface by moving the adsorbed molecule along different axes of the unit cell in order to comprehensively understand perovskite surface structures. This study demonstrates the effectiveness of modifying the perovskite surface structure via a molecular adsorption appr...

35 citations

Journal ArticleDOI
TL;DR: In this article, the anti-Stokes emission within nanometric volumes enables the design of ultracompact, miniaturized photonic devices for a host of applications, such as photonic sensors.
Abstract: Efficient generation of anti-Stokes emission within nanometric volumes enables the design of ultracompact, miniaturized photonic devices for a host of applications. Many subwavelength crystals, suc...

34 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
08 Jun 2001-Science
TL;DR: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated and self-organized, <0001> oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process.
Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 03 nanometer The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis

8,592 citations

Journal ArticleDOI
TL;DR: Physical structure is known to contribute to the appearance of bird plumage through structural color and specular reflection, but a third mechanism, structural absorption, leads to low reflectance and super black color in birds of paradise feathers.
Abstract: Many studies have shown how pigments and internal nanostructures generate color in nature. External surface structures can also influence appearance, such as by causing multiple scattering of light (structural absorption) to produce a velvety, super black appearance. Here we show that feathers from five species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of these feathers (0.05-0.31%) approaches that of man-made ultra-absorbent materials. SEM, nano-CT, and ray-tracing simulations show that super black feathers have titled arrays of highly modified barbules, which cause more multiple scattering, resulting in more structural absorption, than normal black feathers. Super black feathers have an extreme directional reflectance bias and appear darkest when viewed from the distal direction. We hypothesize that structurally absorbing, super black plumage evolved through sensory bias to enhance the perceived brilliance of adjacent color patches during courtship display.

5,916 citations